Electric regulating and control system



Jan. 2, 1945. L. w. THOMPSON 2,366,577

ELECTRIC REGULATING AND CONTROL SYSTEM Filed May 26, 1942 m E 57 Inventor:

Louis W. Thompson, L J 105 His Attorneg Patented Jan. 2, 1945 UNITED STATES PATENT. orric ELECTRIC REGULATING SYSTEM,

also con'raor.

Louis W. Thompson, Schenectady, N. Y., assignmto General Electric Company, a corporation of New York Application May 2c, 1942, Serial No. 144,511

10 Claims. (Cl. 171 -119) My invention relates to electric regulating and I such magnitude as to be unsatisfactory. Various arrangements have been provided for minimizing the hunting action of regulators but many of these have been complicated or have failed to reduce the hunting action as much as desired. In accordance with an important feature of my invention I provide an improved control circuit which is simple, effective and particularly well adapted for anti-hunting purposes and which operates by inserting a controlling influence in an alternating current control circuit in response to a rate of change of a direct current quantity.

It is an object of my invention to provide a new and improved electrical control system.

It is another object o! my invention to provide a new and improved electrical regulating system including an improved anti-hunting circuit.

It is still another object of my invention to provide a new and improved electrical regulating system including an improved anti-hunting circuit for modifying an alternating current control voltage in response to a rate of change of a direct current quantity.

My invention will be better understood by reference to the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

In the drawing Fig. 1 illustrates diagrammatically an embodiment of the invention as applied to a vacuum tube type automatic voltage regulator and Fig. 2 illustrates a modification in which the invention is used in connection with an indirect-acting rheostatic type voltage regulator.

Referring generally to Fig. 1, I provide a regu-v 'lating system for an alternator and associated exciter in which the field winding of the exciter .is energized in accordance with the currentcom to the output voltage oi the alternator. The on? put voltage 01 the alternator is modified in accordance with an anti-hunting voltage bei'oreit is impressed on the voltage responsive bridge; by

means of a rectifier bridge having the direct cur-' rent terminals thereof connected to one winding oi an anti-hunting or stabilizing transformer which has the other winding thereof energized in accordance with the direct current voltage im pressed on the field winding of the alternator by the exciter. In this manner, rate of change of direct current voltage of the exciter induces a voltage in.the transformer which modifies the impedance oi the rectifier bridge tothe flow of alternating current in accordance with the directionand rate of change of the exciter voltage.

In this manner the voltage impressed on the input circuit of the bridge is modified in accordance with the'rate of change ofthe exciter voltage.

Referring now to the details of Fig. 1, I have shown my invention embodied in a regulating system for maintaining the output of an alter-v nating current dynamo-electric machine, such as a generator II, at a desired value. The alternating current generator II has the armature ll connected to supply a three-phase alternating current circuit H. The alternator also includes a field winding I! connected to the armature terminals of an exciter H. Excitation of the exciter is provided by a field winding I 5 connected in series with an adjustable resistance element H and across the terminals 01' the exciter It. The field winding. I5 is also connected in the direct current circuit of a full wave electric valve rectifier circuit illustrated generally by the numeral l1 and comprising electric valve means II and I9; preferably, each of the type comprising an envelope enclosing an ionizable medium such as a gas or vapor and an anode 20, a control member or grid 2| and cathode 22. Each of the electric valve means is also provided with a shield grid 23. The anode-cathode circuits of the elecformer 24 having a midtapped secondary winding 25. As is well understood the direct current circuit of theiull-wave rectifier comprising valves ducted by a pair of electric dischargev valves. The conductivities of the electric discharge valves 1 are controlled by a voltage responsive bridge havli and I9 is connected between the midtap of winding and the cathodes of the two valves which. are electrically connected together. As

illustrated in the drawing, one terminal oi the field winding ll of exciter I4 is connected to the -midpoint of transformer secondary winding 2! ing the inputcircuit thereoi connected to respond 55 by a conductor 28 and the other terminal or th field winding is connected to the cathodes of the electric valves 18, 18 by a conductor 21.

In order that the excitation of the exoiter l4 and as a result the excitation of'the alternator ll may be controlled in accordance with the voltage or other electrical condition of the circuit II, the control members 2| of the valves II and I are energized in accordance with the electrical condition of the circuit I! to be regulated and in the particular arrangement illustrated in accordance with the voltage of the circuit I2. Referring to the drawing, the control members II of electric valves l8 and i9 are energized in accordance with the output of a voltage responsive bridge circuit 28 after it has been amplified by an electric valve amplifier circuit 29. The bridge circuit 28 is provided with alternate arms 34 and 3i comprising linear resistances and the alternate arms 32 and 33 comprising resistance elements having a temperature sensitive resistance characteristic and may be in the form of tungsten filamer t enclosed in a hydrogen filled envelope. A condenser 34 having a variable tap shunting a portion of the resistance arm 3| is provided to modify the output of .the bridge circuit. Diago'rially opposite terminals of the bridge are conneoted across one phase of the circuit 12 while the other diagonally opposite terminals of the bridge are connected to jenergize the primary winding 35 of a transformer 38. The secondary winding 31 of the transformer 38 is connected in series with a source of direct current potential 38 and between the cathode 39 and control member 40 of an electric valve 4|. The valve 4| also includes an anode 42. The anode-cathode circuit of the valve 4i includes a source of direct current voltage 43 and the primary winding 44 of a transformer 45 having a midtapped secondary winding 45 connected to energize the control members ii of electric valve rectifier II. The end terminals of the winding 46 are connected to the control members 2| through current limiting resistors 41 and the midtap of the transformer secondary winding 46 is connected to the cathodes of the electric valves l8 and i9. Suitable filter capacitors 48 are connected across transformer windlugs 31 and 44 to eliminate harmonics from the control voltage impressed on control members It. It is apparent from the foregoing description that the output voltage of the bridge circuit is amplified by means of valve 4| and impressed on the transformer 45 to control the conductivities of the electric valves l8 and [5.

In order to prevent the voltage of the alternator it from fluctuating about a mean value due to overshooting of the regulator circuit, I provide improved means for modifying the operation of the control circuit for the electric valves II and 19 in accordance with the rate of change of voltage of the exciter l4. As illustrated in the drawing, a rectifier bridge 49 preferably comprising units of the dry or contact type is connected in series with one of the input terminals of the voltage responsive bridge 28. The direct current terminals of the bridge are connected to the secondary winding 50 of a stabilizing transformer it having the primary winding 52 thereof connected across the terminals of exciter I4. In this way a voltage is induced in winding 50 proportional to the rate of change of direct current voltage across the terminals of exciter I4. This voltage across the winding 50 impedes the flow of alternating current through the rectifier bridge and in this way effectively varies the alternating current impedance of the rectifier bridge in accordance with the rate of change of exciter voltage. A resistor I! having a variable tap 54 included in series with the rectifier bridge provides means for making an initial adjustment of the regulator system to determine the voltage which the regulator tends to maintain on the lines of the alternating current circuit II.

A better understanding of the features and advantages of my invention may be had by a brief consideration of the operation of the illustrated embodiment described above. As is well understood, the voltage supplied to the alternating current circuit I! by the alternator l0 may be controlled by controlling the energization of the field winding I! of the exciter l4. In the illustrated embodiment this is accomplished by controlling the conductivity of the electric valves II and Il which are connected as a full-wave rectifier and energized from the alternating current circuit i2 and controlled in accordance with the voltage of the circuit I! by means of the voltage responsive bridge ll. The voltage responsive bridge 24 is of a type well known in the art and is usually considered to produce a voltage which varies in magnitude in response to variations in the magnitude of the alternating current voltage impressed thereon and which reverses in phase as the impressed voltage on the bridge circuit goes through a critical value for which the bridge is set. This output voltage is amplified by the amplifier circuit 20 and impressed on the control members it of the valves l8 and 19. The phase relation of the voltages impressed on the valves II, II and the output voltage of the bridge circuit is sith that the valves l4 and I! are rendered fully conductive when the voltage of the circuit I2 is below that for which the bridge is set. When the voltage rises above the value for which the bridge is set, the phase of the output voltage of the bridge circuit 24 reverses and the valves II, I! are rendered nonconducting. In other words, the regulator system works in a manner similar to a vibratory regulator in which the voltage rapidly fluctuates about the value which it is desired to maintain. If desired, gradual variation in conductivity of electric valves II and I. may be obtained if a bias voltage is employed in the circuit of control members 24.

Whether or not the valves are controlled in an on-off manner to operate the regulating system in the manner of a vibratory regulator or whether gradual change in the conductivity of the valves is effected by means of phase shift of the excitation potentials applied to the members 2| is not important to the present invention which relates primarily to the improved anti-hunting circuit for modifying the alternating current voltage of the circuit l2 before it is impressed on the voltage responsive circuit. As mentioned earlier in the description of the apparatus, rectifier bridge 49 is connected in circuit with one of the input terminals of the bridge 28 and has the direct current terminals thereof connected in circuit with the winding 50 of a transformer 52 connected across the terminals of the exciter l4. With this arrangement the voltage impressed on the bridge circuit departs from the voltage of the circuit l2 by an amount dependent upon the voltage drop across the rectifier bridge 49. As is well understood by those skilled in the art the eficct've alternating current impedance of the bridge may be varied by varying the magnitude of the direct current voltage across the direct current terminals of the bridge. The interposition of the transformer 5| between the terminals of the exaseacr/ citer l4 and the direct current terminals of the rectifier circuit 49 makes the variation of impedance of the device 49 responsive to'the rateof change of voltage of the exciter l4 rather than directly responsive 'to the'exciter voltage. The polarity of the exciter with respect to the direct current circuit of the bridge 49 is arranged so that when the direct current voltage of the exciter I4 is decreasing, the voltage induced in winding l5 opposes the fiow of alternating current through the bridge 49 and in this way reduces the voltage impressed on the bridge with respect to the voltage of the alternating current circuit I2. In this way the change in voltage of the circuit I 2'due to the rate of change of voltage of exciter I4 is anticipated and overshooting of the control system is minimized. a

While I have shown my invention embodied in a circuit for controlling the output voltage of an alternator in accordance with the rate of change of the alternator exciter voltage, it will be apparent to those skilled in the art that it is equally suited for other types of control systems where speed or any other quantity is to be controlled or regulated,

In the modification shown in Fig. 2, the voltage of the generator I is regulated by means of an indirect-acting rheostatic voltage regulator of the type described and claimed in my Patent 1,848,852, granted March 8', 1932' and-assigned to the assignee of the present application. This comprises two resistors 55 and 55 connected in series with the field winding l5 of the exciter. The resistance 55 is varied by means of a servo motor 51 so that these two'elements constitute a motor-operated rheostat.- The resistor 56 is a fixed resistor. For normally short circuitlng the resistor 56 there is provided a so-called high speed lowering relay 58 and for short circuitlng the active portion of the rheostatic resistance 55 there is provided a normally openso-called high speed raise contactor 59. The motor and the two high speed relays are controlled in re-- sponse to the voltage of the main generator by means of a regulator head 60 comprising a primary control device in the form of a three-phasetorque motor 6|. This torque motor carries a spring contact assembly comprising low speed raise contact 62, low speed lower contact 63, high speed raise contact 54 and high speed lower con tact 65. The torquev of the motor is balan'cedby a spring 66 so that whenthe regulated quantity is normal the low speed. contacts are substantially equall spaced from a smooth-surfaced rotating common contact 61 and the high speed contacts are similarly substantially equally spaced from a smooth-surfaced rotating common contact 68. These rotating contacts are mounted on a common shaft driven by any suitable means, such as a motor 69. l i

As it isusually undesirable to havethe regulator contacts control directly the current of the motor 51, auxiliary so-called'low speed raise and lower relays l0 and H are connected respectively in circuit with the contacts 62 and 63. The torque motor is energized in accordance with the voltage of the main alternator In by means of an open-delta-connected potential transformer 12.

The alternating current terminals of the bridge-connected rectifier 49 of the anti-hunt ing control system are connected in serieswith' one of the phases of the phase conductors of the torque motor 6|.

In a number of cases there is no convenient source of auxiliary current supply avmhle operating thehighand 'low zspeed .contactomsirhe servo motor .51 or the motor 89 l'or common contacts of the regulator head. devices are theretoresenerglzed x the exciter I 4, although'it'should, :of course, he understood that they could be energized from-:thesmainrgenerator. if desired. In order to insureselisstamtmg of. the :system in itfhas heenashnt is provided a relay "ii-3 connected to respond to the voltage of the main generator having "a normally open :set ol' contacts "which are arranged toshortcircuit the resistance 55 when the malnigenerator voltage isibelow ta predetermined value. I

For controlling :the regulator in response zte watt-less currents in the generator, such acts ctrculating currents 'which ifiow .intthe casecoi parallel-connected generators whose voltages war: not exactlyequal, there .isaprovided'a reactance transformer "14 conmcted in one of the flines of the torque .motor ll. "This sis energizedgproportion .to the currentinxthe corresponding 0! the alternatorxbyicmeans of a current trans- ,iormer 15. y

.The operation offFiE. 21s as follows: "with the voltage of the main generator .at its. normal I value,

the contacts,ottheregulator head wiltallibe :disa

engaged, asrshownyin athe drawing, and the 1.3 will .be picked up. changeszinwdltnge of the ,g'eneratoroccuiaing ,for any reason -"will cause thetorque niotorito respond sons to'malkc either the raise 'or,-.the lower contact, "as the case may be, engage common This will energize aeither =.-the :relay 1'10! the relay ll. thereby to cause "motor -51 *todriw the rheostat in the ,proper direction to restore the voltageto normal. It the change is a melative large one, thelhigh l'speedraise'or'loweroantact, as the, case :may he, vwillcnjgase fits cooperatingcommon contact II, thereby i'to energize fthe corresponding high speed mntactor in which case either the entire resistance .55 will be short circuited so as to cause quick increasein'the excitation and hence the voltage ,or else the normally short circuited resistor 56 willhave circuit removed so as .to' cause rapid decrease i'in the excitationand voltage ofthemain machine. The movingor rotating surfaces of the contacts?! and 68 give a polishingactionof the contact; which insures' an extra longll'ife.

The anti-hunting action i essentially the same as inFig. 11in that whenever there .isa change in voltage-of the exciterlL-a voltage w'lll be induced in the secondary winding 52 of the stabilizing transformer which has "the enact of changing the .Qei'lective impedance between :ithe-rli- /rect current terminals of the rectifier 4! 1nd hence it changes the effective impedanc -between the alternating current terminals of the rectifier. In this manner the effective energization oi' 'the torque motor'li l isvaried in such amannerastto counteract the action'of the regulator :andprevent overshooting orjhunting. a

For bestoperation of this control system the time duration of the transient unidlrectionalvo'ltage inducedin winding .52 should be longhcompared to] the period of a cycle of the main ch cuit I 2. 'This'will always be true for a sixty cycle per second generator having a conventional excitations ystem,

Ah example of a situation where no source'toi' auxiliary currentsupply isavailable 'for operating the regulator motor land its ,contactors 31s where'the generator III is itself thesource c! :aux

iliary supply current in a station or on a ship. Underithese conditions it is imperative that the exciter I4 and the generator ll build up voltagewhenever they .are started from rest. It has been found, however, that in some instances the motor-operated rheostat has been run to its maximum resistance position before the system had previously been shut down so that when it is restarted the field resistance is so high thatselfsistance in the field circuit'of the exciterwhen it is started from rest. It will, therefore, build up voltage so that the regulator can cause the motor 'l'l to operate to lower the resistance of therheostat and can also-cause the high speed raise contactor to short circuit the motor-operated rheostat. Consequently, by the time eighty percent voltage is reached and the relay II opens, the regulator will have taken over control.

The voltage of the reactance transformer I4 is proportional to the current of the alternator II and is substantially in quadrature'with the particular "phase current to which it responds. Therefore, at unity power factor on the alternator Hi this voltage-will be substantially in quadrature with the voltage of the conductor (supplying the torque motorlin which it is inserted; The magnitude of the voltage of'the transformer 14 is small compared to the magnitude of the voltage of this conductor so-that it has negligible eifect on the-regulator under these conditions. 'However, with respect to circulating currents which have a very low power factor and which either lead or lag, depending upon whether the voltage of alternator Iii is below or above other machines with which it may be paralleled, the voltage of the transformer ll will shift its phase so as either to add or subtract from the phase voltage of the torque motor energizing conductor. In this manner the regulator is biased to raise or lower the voltage so as to minimize circulating currents.

While there hasbeen shown and described particular embodiments of thisinvention, it will be obvious to those skilled in the art that various changes and modifications can be made therein without departing from the invention and, therefore, it is aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention,

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electric regulating system for a dynamoelectric machine having a direct current excitation circuit comprising a regulator for controlling the energization of said direct/current excitation circuit, means for energizing said regulator in accordance with an operating condition of said machine comprising a control circuit having'an alternating current voltage which is dependent upon said operating condition, impedance means which is separate from said regulator connected in said control circuit, and means responsive to an electrical condition of said excitation circuit for modifying the effective magnitude of said impedance in a manner to prevent hunting of said regulating system.

2. An electric regulating system for a dynamoelectric machine having a direct current excitation system comprising a regulator, means for controlling the operation of said regulator in accordance with an operating condition of said dynamo-electric machine including a circuit having an alternating voltage which is dependent upon variations in said condition, impedance means which is separate from said regulator connected in said circuit for modifying the effective value of said alternating current voltage, and means responsive to the rate of change of voltage of said direct current excitation circuit for modifying the effective magnitude of said impedance means in a manner to prevent hunting of said regulating system.

3. An electric regulating system for a dynamoelectric machine having a direct current excita tion circuit comprising a regulator operable to produce a variable direct current voltage for energizing said excitation circuit. a control circuit having a variable alternating current voltage which is dependent upon an operating condition of said machine, means for impressing said alternating current voltage on said regulator, and means responsive to the rate of change of said variable direct current voltage for modifying the variable alternating current voltage impressed on said regulator to prevent hunting action of said regulating system.

4. An electric regulating system for apparatus having an operating condition to be controlled, a regulator for producing a variable direct current voltage for controlling said operating condition, a control circuit for producing a variable alternating current voltage in response to variations in said operating condition, and means responsive to the rate of change of said variable direct current voltage for modifying the eifective value of said variable alternating current voltage to prevent hunting action of said regulating systom.

5. An electric regulating system for apparatus having an operating condition to be controlled, a regulator for producing a variable direct current voltage for controlling said operating condition, a control system for controlling the magnitude of said direct current voltage comprising a control circuit responsive to said condition for producing a variable alternating current voltage, impedance means which is separate from said regulator connected in said control circuit, and means for modifying the effective magnitude of said impedance in accordance with changes in said direct current voltage to prevent hunting action Of said regulating system 6. An electric regulating system for apparatus having an operating condition to be controlled, a

regulator for producing a variable direct current voltage for controlling said operating condition, a control system for controlling the magnitude of said direct current voltage comprising a control circuit responsive to said condition for producing a variable alternating current voltage, a rectifier bridge having the alternating current terminals connected in said control circuit, and means for impressing a voltage on the direct current terminals of said bridge dependent upon variations in said direct current voltage to vary the alternating current impedance of said bridge.

7. In an electric regulating system, a dynamoelectric machine having an excitation circuit, an automatic regulator for said machine comprising electric valve means having a control electrode for controlling the voltage of said excitation circuit, an alternating current control circuit energized in accordance with an output condition or said dynamo-electric machine and con nected to energize the control member of said valve means to control the operation thereof in accordance with variations in said condition, impedance means which is separate from said regulator connected in circuit with said alternating current control circuit, and means for modifying the alternating current impedance value of said impedance means in accordance with the rate of change of direct current voltage of said excitation circuit to prevent hunting of said regulating system.

8. In combination, apparatus having an opcrating condition to be regulated, an automatic regulator therefor, said regulator having a. main control circuit connected to be energized in ac cordance with an alternating voltage which is proportional to the value of said condition, a full. wave rectifier having alternating current terrnirials connected in series in said control circuit, said rectifier having a pair of direct current ter minals, and anti-hunting means connected to said direct current terminals for varying the efi voltage build-up of said generator, r

crating condition to be regulated, an regulator therefor, said regulator ha mary controller in the form or" 1:, tin. torque motor connected to be energized by three-phase voltage which is proportional i value of said condition, a fuil rare 'cctiiir ing a pair of alternating current to nin'r s nected in series with one oi the terminals of SL d torque motor. said rectifier having a pair of rect current terminals, and anti-hunting 1' connected between said direct current terrni for effectively varying the impmiance therebe-- tween in accordance with the activity of said regulator.

10.In combination, a dynamo-electric orator, a shunt excited field winding the on in which controls the voltage or said generator, a motor-operated rheost-at connected to co having a high resistance position vviii crgized by said generator for supnly'og current to said motor, an tornatir said generator for controiling said cit a relay responsive to the voltage oi said tor for short circuiting said rheostat Wn voltage. of said generator is substantially predetermined normal value,

LOUIS "W. THQ 

